Because of environmental considerations, the substantial increase in the cost of hydrocarbons, the problem of contamination of the dispensed product by the propellant, and the problem of flammability, there has been considerable research and development activity in recent years to find other expulsion means for aerosol-type and other pressurized dispensers.
For many years there have been manual pump-type dispensers, some of which are still in use, and there have been various attempts to use spring-loaded diaphragms and other mechanical means to provide expulsion pressure, but for several reasons each type has had serious deficiencies. Gaseous media other than the usual freon and freon derivatives and homologs, and isobutane/butane mixtures, have also had their drawbacks, e.g., the required useful pressures have either been too high, depending on the compressibility of the gas, and/or constant dispensing pressure over the useful life of the packaged contents was not possible.
Furthermore, as previously mentioned, it is frequently desirable in some applications that the pressure generating medium not mix in direct contact with the product to be dispensed.
One recent development that has apparently solved the above problems and achieved substantial success is the invention disclosed and claimed in U.S. patent application Ser. No. 105,216 filed Dec. 19, 1979 abandoned in favor of continuation application Ser. No. 223,422, filed on Jan. 8, 1981, owned by the common assignee hereof. The latter invention utilizes a flexible enclosed plastic bag containing an envelope attached to the interior walls of the bag and having pockets carrying one of a two-component gas generating mixture therein which are sequentially opened during expansion of the bag to empty the contents into the bag in admixture with the second gas generating components to generate additional gas. The preferred components are citric acid and sodium bicarbonate which in admixture generate carbon dioxide gas.
In said prior application the bag is fabricated at the point of assembling the aerosol can, and water, sodium bicarbonate and a starting capsule or tablet containing an aliquot of the citric acid are inserted, the bag being heat sealed and inserted into the can just prior to filling the can with the product and sealing of the can.
The present invention is a further extension of the latter concept providing greater utility and flexibility in the manufacture of aerosol-type dispensers and permitting the geographical separation of the various manufacturing operations.